Systemic drug delivery is often ill-suited to the treatment of conditions occurring at one or more discrete sites within a patient's body, because it involves the delivery of the medication to sites other than the target site. Systemic agent delivery also requires the infusion of large doses of the medication to assure the delivery of a therapeutic dose to the target site, thereby creating the possibility of deleterious effects. Another problem of systemic administration is the inevitable fluctuations of drug concentrations that it produces. The dosage that can be delivered to the target site may be limited by the need to minimize unwanted effects in other parts of a patient's body. Furthermore, systemic delivery exposes the medication to possible degradation and elimination by the action of other bodily organs.
Conventional methods of drug therapy, as discussed above, often result in blood levels of the cytotoxic agent that are dangerous for the patient. Even with local administration of these agents, one must consider that blood flow of vessels as well as other transport mechanisms may dilute the local concentration of the therapeutic agent by a wash-out effect. The need remains, therefore, for systems and methods for localized delivery of therapeutic agents, including toxic therapeutic agents, which may be concentrated and localized intramurally within the affected tissue or vessel.
There is general need in many branches of medicine for improved localized internal delivery of substances including therapeutic agents and drugs and diagnostic agents into the walls of ducts, organs and vessels. In particular, there is need for effective systems and methods of delivery into tissue and into cells themselves within organs, ducts, tracts and vessels of the body via percutaneous and luminal access. Problems remain however in the exact method by which the local administration of drugs or therapeutic agents can be achieved. The problem is further complicated where it is desirable to deliver drug in relatively small amounts and the delivery device must be sufficiently small, biocompatible, impermeable and drug non-reactive. There is also a need in some circumstances for retrieval systems and methods of delivery devices which may be implemented at the conclusion of treatment embodiments or portions thereof.